U.S. patent application number 11/532236 was filed with the patent office on 2008-03-20 for apparatus and method for well services fluid evaluation using x-rays.
Invention is credited to Anthony Durkowski, Joel Groves, Rod Shampine, Etienne Vallee, Peter Wraight.
Application Number | 20080069301 11/532236 |
Document ID | / |
Family ID | 38969951 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080069301 |
Kind Code |
A1 |
Shampine; Rod ; et
al. |
March 20, 2008 |
Apparatus and Method for Well Services Fluid Evaluation Using
X-Rays
Abstract
A method and apparatus for determining the density and phase
fractions of well services fluids is shown including an x-ray
generator, a sample cell, and a radiation detector. Radiation is
passed through the sample cell and fluid and the attenuated
radiation signal is used to evaluate the fluid. In one embodiment,
a reference radiation detector measures a filtered radiation signal
and controls the acceleration voltage and/or beam current of the
x-ray generator using this information. The apparatus may be
permanently affixed for long term monitoring or temporarily clamped
on to a pipe in production.
Inventors: |
Shampine; Rod; (Houston,
TX) ; Groves; Joel; (Leonia, NJ) ; Durkowski;
Anthony; (Lawrenceville, NJ) ; Vallee; Etienne;
(Princeton, NJ) ; Wraight; Peter; (Skillman,
NJ) |
Correspondence
Address: |
SCHLUMBERGER TECHNOLOGY CORPORATION;David Cate
IP DEPT., WELL STIMULATION, 110 SCHLUMBERGER DRIVE, MD1
SUGAR LAND
TX
77478
US
|
Family ID: |
38969951 |
Appl. No.: |
11/532236 |
Filed: |
September 15, 2006 |
Current U.S.
Class: |
378/53 |
Current CPC
Class: |
G01N 2015/0693 20130101;
G01N 9/24 20130101; G01N 23/083 20130101; G01N 33/2823 20130101;
G01N 23/12 20130101 |
Class at
Publication: |
378/53 |
International
Class: |
G01N 23/06 20060101
G01N023/06 |
Claims
1. A tool for determining at least one physical property of a well
services fluid comprising: an x-ray generator; an input radiation
emitted by said x-ray generator; a housing containing a well
services fluid; an output radiation generated by passing said input
radiation through said housing and said well services fluid; a
measurement radiation detector configured to measure said output
radiation and produce a measurement signal; and an analysis unit,
said analysis unit being configured to determine a physical
property of said well services fluid using said measurement
signal.
2. The tool of claim 1, wherein said analysis unit determines said
at least one physical property by measuring an attenuation of said
input radiation.
3. The tool of claim 1, further comprising: a reference radiation
generated by altering said input radiation; a reference radiation
detector being configured to measure the reference radiation and
produce a reference signal; and said analysis unit further being
configured to control at least one of an acceleration voltage and a
beam current of said x-ray generator using said reference
signal.
4. The tool of claim 1, further comprising: a reference radiation
generated by altering said input radiation; a reference radiation
detector being configured to measure the reference radiation and
produce a reference signal; and wherein said analysis unit
determines said at least one physical property by comparing said
reference signal to said measurement signal.
5. The tool of claim 3, further comprising a filter, wherein said
reference radiation is generated by passing said input radiation
through said filter.
6. The tool of claim 3, wherein said reference radiation comprises
at least one low energy region and at least one high energy
region.
7. The tool of claim 6, wherein said acceleration voltage of said
x-ray generator is controlled by a ratio of a high energy count to
a low energy count detected at said reference radiation
detector.
8. The tool of claim 6, wherein said beam current of said x-ray
generator is controlled by one of a high energy count, a low energy
count, or a sum of a high energy count and low energy count, said
high energy count and low energy count being detected at said
reference radiation detector.
9. The tool of claim 5, wherein said filter comprises gold
(Au).
10. The tool of claim 1, wherein said housing is a well pipe, and
wherein said x-ray generator and said measurement radiation
detector are removably attached to said well pipe.
11. The tool of claim 1, wherein said well services fluid is a
fluid selected from the group consisting of a fracturing fluid and
a cement slurry.
12. The tool of claim 11, wherein said at least one property is a
property selected from the group consisting of density, and one or
more phase fractions.
13. (canceled)
14. (canceled)
15. A tool for analysis of a well services fluid comprising: an
x-ray generator; an input radiation emitted by said x-ray
generator; a housing containing a well services fluid; an output
radiation generated by passing said input radiation through said
housing and said well services fluid; a measurement radiation
detector being configured to measure said output radiation and
produce a measurement signal; a reference radiation generated by
altering said input radiation; a reference radiation detector being
configured to measure said reference radiation and produce a
reference signal; an analysis unit, said analysis unit being
configured to determine at least one physical property of said well
services fluid by comparing said reference signal to said
measurement signal; and said analysis unit further being configured
to control at least one of an acceleration voltage and a beam
current of said x-ray generator using said reference signal.
16. The tool of claim 15, further comprising a filter; wherein said
reference radiation is generated by passing said input radiation
through said filter.
17. The tool of claim 15, wherein said reference radiation
comprises at least one low energy region and at least one high
energy region.
18. The tool of claim 17, wherein said acceleration voltage is
controlled by a ratio of a high energy count detected at said
reference detector to a low energy count detected at said reference
detector.
19. The tool of claim 17, wherein said beam current of said x-ray
generator is controlled by one of a high energy count, a low energy
count, or a sum of a high energy count and a low energy count, said
high energy count and said low energy count being detected at said
reference radiation detector.
20. The tool of claim 15, wherein said well services fluid is a
fracturing fluid comprising a mixture of water and proppant, and
wherein said at least one physical property is a density.
21. The tool of claim 15, wherein said well services fluid is a
cement slurry, and wherein said at least one physical property is
one or more phase fractions.
22. A method for determining a physical property of a well services
fluid comprising: generating an input radiation using an x-ray
generator; passing said input radiation through a well services
fluid to produce an output radiation; and determining at least one
physical property by comparing said input radiation to said output
radiation, and measuring an attenuation of said input radiation
signal.
23. The method of claim 22, further comprising filtering said input
radiation to create a reference radiation wherein said reference
radiation comprises at least one low energy region and at least one
high energy region.
24. The method of claim 23, further comprising: detecting said
reference radiation; and creating a high energy reference count and
a low energy reference count.
25. The method of claim 24, further comprising controlling an
acceleration voltage of said x-ray generator based on a ratio of
said high energy reference count to said low energy reference
count.
26. The method of 24, further comprising controlling a beam current
of said x-ray generator based on one of said low energy reference
count, said high energy reference count, and a sum of said low
energy reference count and said high energy reference count.
27. (canceled)
28. (canceled)
29. (canceled)
30. The method of claim 22, wherein said method is performed during
an oil well selected from the group consisting of a fracturing
operation and a cementing operation.
31. (canceled)
Description
BACKGROUND
[0001] This disclosure relates to an apparatus and method for
evaluating fluids encountered in a well services context using
x-rays. More specifically, this disclosure relates to a system for
using x-rays to determine the density and phase fractions of a well
services fluid such as a fracturing fluid, a cement slurry, a
mixture of drilling mud and cuttings, or any other fluid that may
be encountered. These measurements are generally taken above ground
using an x-ray generator and a measurement radiation detector with
the fluid of interest being housed in a pipe. Additionally, a
second reference radiation detector may be used that detects a
filtered signal from the x-ray generator and controls an
accelerating voltage and a beam current of the x-ray generator.
[0002] It is common in the recovery of hydrocarbons from
subterranean formations to fracture the hydrocarbon-bearing
formation to provide flow channels through which the desired fluid
can be obtained. In such operations, a fracturing fluid is injected
into a wellbore penetrating the subterranean formation and is
forced against the formation strata by pressure. The formation
strata or rock is forced to crack or fracture, and a proppant is
placed in the fracture by movement of a viscous fluid containing
proppant into the crack of the rock. The resulting fracture, with
proppant in place, provides improved flow of the recoverable fluid,
i.e., oil, gas, or water, into the wellbore.
[0003] Fracturing fluids often comprise a thickened or gelled
aqueous solution which has suspended therein proppant particles
that are substantially insoluble in the fluids of the formation.
Proppant particles carried by the fracturing fluid remain in the
fracture created, thus propping open the fracture when the
fracturing pressure is released and the well is put into
production. Suitable proppant materials include sands (silicon,
ceramic, resin), walnut shells, sintered bauxite, glass beads,
salts, or similar materials. The propped fracture provides a larger
flow channel to the wellbore through which an increased quantity of
hydrocarbons can flow.
[0004] In the industry, it is desirable to monitor the quality of
the fluid within the system. This includes monitoring the
concentration of particulates within the fluid. Current methods for
controlling the quality of the addition of particulates include:
pre and post-job batch weighing, mechanical metering during the
addition of particulates, or radioactive measurements of the fluid
slurries during operations.
[0005] Batch weighing provides quality control of the cumulative
total product used, but does not provide quality control during on
the fly operations for pre-engineered programs that vary the rate
at which particulates are added during different phases of the
injection.
[0006] Mechanical metering involves measuring the rate at which the
particulate is added and the rate of the fluid prior to addition
(clean rate) and then using these rates to calculate the
particulate concentration of the slurry. The calculation for
concentration is based on the knowledge of the density of the fluid
and the particulate material. However, mechanical metering is prone
to slippage and inaccuracies due to the efficiencies of the
mechanical system being employed. The quality of the measurement is
therefore limited.
[0007] The density of fracturing fluids has been determined using
radioactive systems as well. Specifically, gamma-ray densitometers
are currently used in the oilfield for controlling the proppant
mass balance in fracturing jobs. The basic measurement is the
attenuation of Cesium (Cs.sup.137) 662 keV gamma-rays by the
fracturing fluid. With proper calibration and data processing, the
proppant mass balance error is in the range of 1-2%. This type of
system takes a single measurement of the radiation flux reaching
the detector and determines a density from this measurement.
[0008] While this type of system can provide an accurate result,
there are drawbacks to the use of a chemical source such as
Cs.sup.137 in measurements in the field. Any radioactive source
carries high liability and strict operating requirements. These
operational issues with chemical sources have led to a desire to
utilize a safer radiation source. Although the chemical sources do
introduce some difficulties, they also have some significant
advantages. Specifically, the degradation of their output radiation
over time is stable allowing them to provide a highly predictable
radiation signal. An electrical radiation generator would alleviate
some of these concerns, but most electrical photon generators (such
as x-ray generators) are subject to issues such as voltage and beam
current fluctuation. If these fluctuations can be controlled, this
would provide a highly desirable radiation source.
[0009] In addition to measuring the density of fracturing fluid, it
is also useful to measure properties of other fluids utilized in
the oilfield. For instance, when production on a well comes to a
close, it is necessary to fill the well with a cement slurry to
stabilize the remaining fractures surrounding the well. It is
desirable to use the same tool used for fracturing fluid density
determination to determine the phase fractions of water and cement
in the cement slurry. Prior art systems for phase fraction
determination have also utilized chemical sources which may not be
desirable for the reasons detailed above.
[0010] Accordingly, a need has been identified for a tool that may
be used to determine properties of any fluid encountered in the
well services context. One specific example is to measure the
density of fracturing fluid employing an electrical photon
generator such as an x-ray generator. This generator must be stable
over time with its parameters closely controlled to ensure accurate
measurements regardless of changing conditions. Additionally, it is
desired to use the same system to determine the phase fractions of
cement and water in a cement slurry or the characteristics of any
other well services fluid that may be encountered.
BRIEF SUMMARY OF THE INVENTION
[0011] In consequence of the background discussed above, and other
factors that are known in the field of fracturing fluid density
determination, applicants recognized a need for an apparatus and
method for determining properties of fluids collected in a well
services environment. Applicants recognized that an x-ray generator
with a carefully controlled acceleration voltage and beam current
could be used along with one or more radiation detectors to provide
a reliable measure of the characteristics of a host of fluids.
[0012] One embodiment comprises a method and apparatus for
determining the density of a fracturing fluid. In one aspect, an
x-ray generator provides radiation input that is attenuated by a
fracturing fluid in a pipe. The attenuated radiation is measured
and a density of the fracturing fluid is determined. Additionally,
the radiation output by the x-ray generator may be filtered to
produce a high energy region and a low energy region, this spectrum
being introduced to a radiation detector. The output of this
radiation detector is used to control the acceleration voltage and
beam current of the x-ray generator.
[0013] Another embodiment of the present invention allows for the
determination of the phase fractions of water and cement in cement
slurry. Again, radiation is introduced to a pipe through which the
cement slurry is passing; the readings of a radiation detector are
used to calculate the phase fractions.
[0014] The present invention is useful on any fluid encountered and
is not limited to the two specific examples detailed herein.
THE DRAWINGS
[0015] The accompanying drawings illustrate embodiments of the
present invention and are a part of the specification. Together
with the following description, the drawings demonstrate and
explain principles of the present invention.
[0016] FIG. 1 is a schematic view of the operational context in
which the present apparatus and method can be used to
advantage;
[0017] FIG. 2 is a graphic representation of a radiation energy
spectrum output by an x-ray generator;
[0018] FIG. 3 is a schematic representation of one embodiment of
the present invention;
[0019] FIG. 4 is a schematic representation of another embodiment
of the present invention comprising a reference detector;
[0020] FIG. 5 is a schematic representation of another embodiment
of the present invention comprising a reference detector and a
window in the wall of the pipe.
[0021] FIG. 6 is a graphic representation of a filtered radiation
spectra used in control of an x-ray generator.
[0022] FIG. 7 is a schematic representation of one embodiment of an
x-ray tube;
[0023] FIG. 8 is a schematic representation of a radiation detector
that may be used;
[0024] FIG. 9 is a schematic representation of the general
structure of one embodiment of the invention;
[0025] FIG. 10 is a detailed schematic of one embodiment of the
invention operable for clamping on to a pipe.
DETAILED DESCRIPTION
[0026] Referring now to the drawings and particularly to FIG. 1
wherein like numerals indicate like parts, there is shown a
schematic illustration of an operational context 100 of the instant
invention. This figure shows one example of an application of the
invention for determining the density of fracturing fluids. The
invention is applicable to any well services fluids and this is
being described as one example. As described above, fracturing
fluid generally comprises a fluid being mixed with a solid
proppant. Proppant source 102 supplies solid material while fluid
source 104 provides the fluid base for the fracturing fluid. The
proppant and fluid is mixed at point 110 to become fracturing
fluid.
[0027] In one embodiment, a device for determining the density of
the fracturing fluid is clamped on to the pipe. Cuff 114 is
connected by the connection mechanism 116. Not pictured is an
opposing hinge or other connection mechanism that allows the device
to be opened and placed on or removed from the pipe. X-ray
generator 112 creates radiation that is passed through the pipe as
well as its contents. The resulting radiation signal is measured by
measurement radiation detector 118. The radiation output from x-ray
generator 112 is measured by reference radiation detector 120. The
information from these detectors is then used to determine the
density of the fracturing fluid and, if an optional reference
radiation detector is used, to control the acceleration voltage and
beam current of x-ray generator 112.
[0028] Some examples of scenarios in which this invention is
advantageous include permanent monitoring, mobile testing,
laboratory testing, and artificial lift optimization. Those of
ordinary skill in the art will recognize that these are merely
examples of possible uses and the above examples are not
exhaustive.
X-Ray Physics
[0029] X-ray tubes produce x-rays by accelerating electrons into a
target via a high positive voltage difference between the target
and electron source. The target is sufficiently thick to stop all
the incident electrons. In the energy range of interest, the two
mechanisms that contribute to the production of x-ray photons in
the process of stopping the electrons are X-ray fluorescence and
Bremsstrahlung radiation.
[0030] X-ray fluorescence radiation is the characteristic x-ray
spectrum produced following the ejection of an electron from an
atom. Incident electrons with kinetic energies greater than the
binding energy of electrons in a target atom can transfer some
(Compton Effect) or all (Photoelectric Effect) of the incident
kinetic energy to one or more of the bound electrons in the target
atoms thereby ejecting the electron from the atom.
[0031] If an electron is ejected from the innermost atomic shell
(K-Shell), then characteristic K, L, M and other x-rays are
produced. K x-rays are given off when an electron is inserted from
a higher level shell into the K-Shell and are the most energetic
fluorescence radiation given off by an atom. If an electron is
ejected from an outer shell (L, M, etc.) then that type of x-ray is
generated. In most cases, the L and M x-rays are so low in energy
that they cannot penetrate the window of the x-ray tube. In order
to eject these K-Shell electrons, an input of more than 80 kV is
required in the case of a gold (Au) target due to their binding
energy.
[0032] Another type of radiation is Bremsstrahlung radiation. This
is produced during the deceleration of an electron in a strong
electric field. An energetic electron entering a solid target
encounters strong electric fields due to the other electrons
present in the target. The incident electron is decelerated until
it has lost all of its kinetic energy. A continuous photon energy
spectrum is produced when summed over many decelerated electrons.
The maximum photon energy is equal to the total kinetic energy of
the energetic electron. The minimum photon energy in the observed
Bremsstrahlung spectrum is that of photons just able to penetrate
the window material of the x-ray tube.
[0033] The efficiency of converting the kinetic energy of the
accelerated electrons into the production of photons is a function
of the accelerating voltage. The mean energy per x-ray photon
increases as the electron accelerating voltage increases.
[0034] A Bremsstrahlung spectrum can be altered using a filter and
by changing (1) the composition of the filter, (2) the thickness of
the filter, and (3) the operating voltage of the x-ray tube. One
embodiment described herein utilizes a single filter to create low
and high energy peaks from the same Bremsstrahlung spectrum.
Specifically, a filter is used to provide a single spectrum
measured by a reference radiation detector with a low energy peak
and a high energy peak.
[0035] FIG. 2 shows a Bremsstrahlung radiation spectrum 206 that
may be employed in the instant invention. Ordinate axis 202
represents energy measured in keV. Abscissa axis 204 is the count
rate or the number of photons per second per keV that are incident
on a radiation detector. This input radiation is filtered as
described above.
Fracturing Fluid Densitometer
[0036] One example of a use for the invention in a well services
environment is determining the density of a fracturing fluid. The
density of a material can be obtained by measuring the attenuation
of radiation passed through that material. In addition, if the
fluid is a two phase fluid, the same measurement can be used to
determine the phase fractions of the fluid. In the instance of most
well services fluids, in one embodiment, the radiation must pass
through one pipe wall, the fluid, and another pipe wall before
being measured by a radiation detector. Due to this, a relatively
high energy radiation signal is used. Specifically, the pipes are
generally made of steel (largely consisting of iron) which has a
mass attenuation coefficient that is nearly independent of energy
above 200 keV. Consequently, 200 keV photons penetrate the walls of
an iron pipe almost as easily as the 662 keV gamma rays emitted
from a Cesium (.sup.137Cs) or the 1332 keV gamma rays from Cobalt
(.sup.60Co). This benefits the system because the 200 keV signal
from an x-ray generator can be more effectively shielded making the
system more stable and eliminating the disadvantages of using a
chemical radiation source.
[0037] Although they provide a number of advantages, unlike
chemical sources, all x-ray generators are susceptible to
degradation of performance over time. For this reason, in one
embodiment, a reference radiation detector is used to control the
beam current and acceleration voltage of the x-ray generator.
[0038] The density of a material can be determined by analyzing the
attenuation of x-rays passed through the material. The initial
measurement to be found is not the mass density, .rho., that will
be the eventual product, but the electron density index,
.rho..sub.e, of the material. The electron density index is related
to the mass density by the definition
.rho. e = 2 Z A .rho. ##EQU00001##
[0039] The attenuation of a beam of x-rays of energy E, intensity
I.sub.0(E), passing through a thickness `d` of material with a
density `.rho..sub.e` can be written
I ( E ) = I 0 ( E ) e - .mu. m ( E ) .rho. e Ad 2 Z
##EQU00002##
where any interaction of the photons traversing the material
attenuates the beam. Here, .mu..sub.m(E) is the mass attenuation
coefficient of the material. It is important to note that this mass
attenuation coefficient is variable depending on the type of fluid
that is present. To find the value, calibration testing is often
performed or, alternatively, a series of calculations is made based
on the known chemistry of the fluid that is present. I(E) in the
previous equation does not include the detection of photons created
following photoelectric absorption or multiple scattered photons.
In the case of most well services fluids, the mass attenuation
coefficients of each phase will be known. However, if necessary,
these values may be found by calculations or calibration tests
using this system.
[0040] Turning to FIG. 3, one embodiment of the invention is shown.
In this embodiment, x-ray generator 302 creates a spectrum like the
one shown in FIG. 2. This radiation is passed through one wall of
the pipe 306. A well services fluid flows through the inside 305 of
the pipe 306. The radiation then passes through the well services
fluid and through the opposite wall of pipe 306. The resulting
radiation signal is measured by radiation detector 308. The output
of radiation detector 308 is then passed along line 317 to analysis
unit 318. Analysis unit 318 utilizes the output of radiation
detector 308 to determine the density of the well services fluid as
detailed below.
[0041] FIG. 4 shows another embodiment of the invention. In this
embodiment, x-ray generator 402 creates a spectrum like the one
shown in FIG. 2. This radiation is passed through one wall of the
pipe 404. Well services fluid flows through the inside 405 of the
pipe 404. The radiation passes through the well services fluid and
through the opposite wall of pipe 404. The resulting radiation
signal is measured by measurement radiation detector 408. The
output of radiation detector 408 is then optionally passed to an
analysis unit 412.
[0042] In addition to measurement radiation detector 408, reference
radiation detector 410 measures the output of x-ray generator 402
directly. The purpose of this reference detector 410 is to control
the beam current and acceleration voltage of x-ray generator 402.
Analysis units 412 and 418, connected by line 417, receive the
output signals of the radiation detectors and perform the
calculations described herein.
[0043] In order to correctly control these values, the radiation
signal must be filtered by filter mechanism 406. Any high-Z
material can be used to filter the input radiation spectrum and
produce the dual peak spectrum that is desired. In one embodiment,
the filter is gold (Au) and produces the spectrum shown in FIG. 6,
other possible materials include, but are not limited to, lead
(Pb), tungsten (W), bismuth (Bi), and mercury (Hg). In this figure,
Abscissa axis 602 represents energy measured in keV. Ordinate axis
604 is the count rate or the number of photons per second per keV
that are incident on a radiation detector. Trace 608 represents a
low energy region of the signal, trace 610 represents a high energy
region of the signal. The reference radiation detector bins the
radiation into two windows, a high energy window with all counts at
an energy higher than point 606 and a low energy window with all
counts at an energy lower than point 606. The high energy count is
referred to as I.sub.R.sub.H while the low energy count is referred
to as I.sub.R.sub.L.
[0044] As mentioned above, the counts at the reference radiation
detector are used to control the acceleration voltage and beam
current of x-ray generator 402. This is necessary because any x-ray
generator is subject to electrical fluctuations that could cause
error in the resultant density calculation. The I.sub.R.sub.H and
I.sub.R.sub.L are both proportional to the number of electrons
hitting the target at any given time. Additionally, the ratio
of
I R H I R L ##EQU00003##
is proportional to the acceleration voltage of the x-ray generator
V.sub.x-ray. Looking at FIG. 6, if the voltage of the x-ray
generator decreased over time, the spectrum would shift somewhat to
the left. This would cause less electrons to be placed in the high
energy window and thus the ratio
I R H I R L ##EQU00004##
would decrease. This embodiment avoids this problem by monitoring
this ratio, possibly in unit 412, and altering the acceleration
voltage of the x-ray generator 402 to maintain a consistent
spectrum.
[0045] In addition, it is important to carefully control the beam
current output by the x-ray generator. This can also be controlled
using the reference detector. The reference detector counts the
number of incident photons in the high energy region and low energy
region. The output of the reference detector can be used by either
monitoring one of these counts or the sum of the two counts. The
output of the reference detector is used to control the x-ray
generator and ensure a constant beam current.
[0046] Another embodiment using a reference detector is shown in
FIG. 5. In this embodiment, a filter 504 is placed at the output of
x-ray generator 502 to produce a signal like that shown in FIG. 6.
The signal is passed through a window in pipe 506, through the well
services fluid on the inside 505 of the pipe 506, and out through
another window in pipe 506. The output radiation is measured by
measurement radiation detector 508. The filtered radiation signal
is also measured by reference radiation detector 510 for
controlling the acceleration voltage and beam current of x-ray
generator 502 as described above. Analysis units 512 and 518,
connected by line 517, receive the output signals of the radiation
detectors and perform the calculations described herein. This
embodiment is useful when determining the phase fractions of a
fluid having three phases. The method for this can be found in U.S.
patent application Ser. No. 11/425,285 assigned to Schlumberger
Technology Corporation and hereby incorporated by reference as
though set forth at length.
[0047] FIG. 7 shows an example of an x-ray tube 700 that may be
used. Note that any x-ray tube may be used provided that the
acceleration voltage and beam current can be controlled. Element
702 is a cathode that is operable to release electrons in response
to exposure to heat. The introduction of a small current heats the
cathode 702 and causes it to release electrons. Grid 704 is
operable to move electrons released from cathode 702 toward
electron accelerating section 706. In one embodiment, this grid 704
is made of Nickel (Ni). Accelerating section 706 speeds electrons
toward target 708. In one embodiment, this target is gold (Au.)
Upon collision with target 706, tube 700 generates x-rays suitable
for use in the instant invention.
[0048] Radiation detectors 308, 408, 410, 508, and 510 may be any
type of radiation detector that is capable of monitoring incident
radiation and producing an output signal corresponding to that
radiation. Generally, the type of radiation detector used comprises
a scintillating material interfaced with a photocathode and
electron multiplier. One example of a radiation detector that may
be used is described in U.S. patent application Ser. No. 09/753,859
assigned to Schlumberger Technology Corporation and herein
incorporated by reference as though set forth at length. This
radiation detector is illustrated in FIG. 8. Radiation detector 800
comprises an optical window 802 and an attached window housing 804,
a primary cylinder 808 having an attached radiation entry window
806, a scintillator crystal 807 and a closing plate 810. The
optical window 802 will typically be made of a glass or sapphire
plate. The outer housing of the detector will usually be made of a
glass sealing alloy such as Kovar. This type of detector is
advantageous because it corrects its function with changing
temperatures and conditions. This ensures that a constant reading
can be obtained in any working environment.
[0049] FIG. 9 shows the general physical layout of the fracturing
fluid densitometer. Pipe 901 transports fracturing fluid 906 and
may be either a test pipe or a production pipe actively inserting
or removing well services fluid into a borehole. X-ray generator
902 emits radiation signal 904 through the first wall of pipe 901,
the fracturing fluid, and the second wall of pipe 901. The
resulting radiation signal is measured by measurement radiation
detector 908. Reference radiation detector 910 measures the output
of x-ray generator 910 for controlling its acceleration voltage and
beam current as described above.
[0050] FIG. 10 is a detailed schematic of one embodiment of the
invention. Well services fluid 1004 flows through pipe 1003. The
invention attaches to pipe 1003 via clamping housing 1001 which is
connected at connection mechanism points 1002. In one embodiment,
this connection mechanism is a bolt on type that secures the clamp
on both sides. X-ray generator 1005 comprises x-ray tube 1006 and
associated hardware. Blind flanges 1010 enclose the x-ray tube and
ensure that radiation is not released. Shock absorbers 1008 dampen
the vibration encountered by the x-ray tube. Tungsten cap 1014
provides shielding. Reference radiation detector 1016 measures the
output from x-ray tube 1006 while measurement radiation detector
1018 measures the radiation that has passed through the pipe 1003
and fracturing fluid 1004.
[0051] The density of a mixture, .rho..sub.mix, of two immiscible
materials, solid S with density .rho..sub.S and liquid L with
density .rho..sub.L is given by
.rho..sub.mix=.rho..sub.Sf.sub.S+.rho..sub.Lf.sub.L=.rho..sub.Sf.sub.S+.-
rho..sub.L(1-f.sub.S)
Where f.sub.S is the volume fraction V.sub.S/V.sub.T, of the solid,
and f.sub.L is the volume fraction V.sub.L/V.sub.T of the liquid,
where V.sub.T=V.sub.S+V.sub.L.
[0052] Proppant slurries are specified by the proppant
concentration P.sub.C, the mass of the solid proppant added to a
given volume of the fluid. P.sub.C can be represented by
P C = M S V L = .rho. S f S 1 - f S . ##EQU00005##
Using this, the density of the mixture can be written in terms of
the proppant concentration
[0053] .rho. mix = .rho. S ( P C + .rho. L ) P C + .rho. S .
##EQU00006##
[0054] The standard units for the proppant concentration are pounds
of proppant per gallon of fluid while the density is generally
expressed in mass per unit volume (gm/ml.) The equation above can
be altered to account for these units as follows
.rho. mix = .rho. S ( P C + 8.34 .rho. L ) P C + 8.34 .rho. S
##EQU00007##
and similarly,
P C = M S V L = 8.34 .rho. S f S 1 - f S ##EQU00008##
thus providing the density of the mixture.
Cement Slurry Phase Fraction Determination
[0055] Another use for the instant invention is the determination
of the phase fraction of a two phase well services fluid. In order
to determine the phase fractions of the components of a two phase
sample, such as cement slurry, attenuation measurements are taken
using the subject invention. The measurement corresponds to the
following equation
I.sub.M=I.sub.M.sup.(0)e.sup.-(.mu..sup.1.sup.d.alpha..sup.1.sup.+.mu..s-
up.2.sup.d.alpha..sup.2.sup.)
where I.sub.M is the number of counts detected by a measurement
radiation detector, I.sub.M.sup.(0) is the number of counts when
the radiation is passed through the empty sample cell, d is the
diameter of the sample cell, .alpha..sub.1 is the fluid phase
fraction of the first fluid constituent such as proppant, and
.alpha..sub.2 is the fluid phase fraction of the second
constituent, such as water. These fractions are unknown and are the
subject of interest. This equation can be solved to provide the
following
- ln ( I M I M ( 0 ) ) = .mu. 1 d .alpha. 1 + .mu. 2 d .alpha. 2 .
##EQU00009##
At this point, there is a single equation with two unknowns, so a
further equation is needed to solve for the fluid fractions. The
sample fluids comprise two phases, so it is also known that
.alpha..sub.1+.alpha..sub.2=1.
Using these two equations, the fluid fractions of the two
components making up the well services fluid can be determined
based on the radiation passed through the sample.
[0056] The phase fraction is especially important in the case of
cement slurry where it is necessary to get the correct ratio of
water to solid. In some cases, a cement slurry with have a gas
injected into it creating a third phase that must be determined.
This can be done in one of two ways. The first method is to do as
above and first determine the phase fraction of solid and liquid
before injecting the gas. Once the gas is injected, the same
measurement can be performed knowing that one phase is the
solid/liquid mix and the other phase is the gas. This gives the
relative amount of each phase and allows for determine of the three
phase fractions.
[0057] An alternative to this method is to use the configuration
shown in FIG. 5. In this configuration, a filtered radiation signal
such as that shown in FIG. 6 is sent through the three phase fluid
of interest. The measurement radiation detector takes a measurement
in the high energy region and the low energy region and bins the
resulting radiation into a high energy count and a low energy
count. The high energy measurement corresponds to the following
equation
I.sub.M.sub.H=I.sub.M.sub.H.sup.(0)e.sup.-(.mu..sup.1.sup.d.alpha..sup.1-
.sup.+.mu..sup.2.sup.d.alpha..sup.2.sup.+.mu..sup.3.sup.d.alpha..sup.3.sup-
.)
where I.sub.M.sub.H is the number of high energy counts detected by
a measurement radiation detector, I.sub.M.sub.H.sup.(0) is the
number of high energy counts when the radiation is passed through
the empty sample cell, d is the diameter of the sample cell,
.alpha..sub.1 is the fluid phase fraction of a first phase,
.alpha..sub.2 is the fluid phase fraction of a second phase, and
.alpha..sub.3 is the fluid phase fraction of a third phase. These
fractions are unknown and are the subject of interest. The low
energy measurement corresponds to the following equation
I.sub.M.sub.L=I.sub.M.sub.L.sup.(0)e.sup.-(.mu..sup.1.sup.d.alpha..sup.1-
.sup.+.mu..sup.2.sup.d.alpha..sup.2.sup.+.mu..sup.3.sup.d.alpha..sup.3.sup-
.)
where I.sub.M.sub.L is the number of low energy counts detected by
a measurement radiation detector and I.sub.M.sub.L.sup.(0) is the
number of low energy counts when the radiation is passed through
the empty sample cell. Both of these equations can be solved to
provide the following
- ln ( I M H I M H ( 0 ) ) = .mu. 1 d .alpha. 1 + .mu. 2 d .alpha.
2 + .mu. 3 d .alpha. 3 ##EQU00010##
for the high energy measurement and
- ln ( I M L I M L ( 0 ) ) = .mu. 1 d .alpha. 1 + .mu. 2 d .alpha.
2 + .mu. 3 d .alpha. 3 ##EQU00011##
for the low energy signal. Solving for both the high energy and low
energy measurements, this provides two equations and three
unknowns, so a further equation is needed to solve for the fluid
fractions. The sample fluids comprise three phases, so it is also
known that
.alpha..sub.1+.alpha..sub.2+.alpha..sub.3=1.
Using these three equations, the fluid fractions of all three
phases can be determined based on the radiation passed through the
sample. One example is the phase fractions of water, solid, and gas
in a cement slurry.
[0058] The application of this invention is not limited to the
fluids specifically enumerated above. Any fluid encountered in a
well services environment may be evaluated for density and phase
fractions using the structures and methods detailed herein. The
tool is powerful because it utilizes a safe source of radiation and
is highly portable allowing for temporary or permanent testing in
the field with a low level of risk.
[0059] The preceding description has been presented only to
illustrate and describe the invention and some examples of its
implementation. It is not intended to be exhaustive or to limit the
invention to any precise form disclosed. Many modifications and
variations are possible and would be envisioned by one of ordinary
skill in the art in light of the above description and
drawings.
[0060] The various aspects were chosen and described in order to
best explain principles of the invention and its practical
applications. The preceding description is intended to enable
others skilled in the art to best utilize the invention in various
embodiments and aspects and with various modifications as are
suited to the particular use contemplated. It is intended that the
scope of the invention be defined by the following claims; however,
it is not intended that any order be presumed by the sequence of
steps recited in the method claims unless a specific order is
directly recited.
* * * * *